MIDDLE AND UPPER ORDOVICIAN. 195 



lacking, the contact with the " Calciferous " (lowermost Ordovician) or the pre- 

 Cambrian, upon which it overlaps. The passage from the "Trenton" limestone or 

 dolomite to the overlying shale described by Lane as the Utica is well marked litho- 

 logicaUy. Lane states the thickness of the "Trenton" as 250 to 271 feet. It is 

 in places dolomitic. Subdivisions in the Green Bay region are recognized by him 

 as follows : 



Galena limestone: Feet. 



[Limestone,] crystalline, granular 83 



Limestone, fossilif erous 55 feet, white 8 feet, dark 9 feet 72 



Alternating blue and brown, crystalline, granular. With the dark base compare the Wis- 

 consin oil rock 225 



Sandy limestones, ' ' quartz " 6 feet, limestone 44 feet, quartz 1 foot, limestone 24 feet; compare 



quartz sandstone at Marinette at 260-275 feet 75 



Wisconsin Trenton (Platteville?), blue shale and limestone (blue shale 4 feet, black limestone 



141 [14?] feet, limestone 19 feet, blue shale 4 feet) 41 



The formation recognized by Lane as the Utica shale is described as a black 

 shale ranging in thickness from 50 feet at the north to about 200 feet at the south. 

 The formation described by him as Lorraine or MaysviUe is an abundantly fossilif- 

 erous blue shale which he correlates with the Maquoketa of Iowa. 



Lane groups certain coarser deposits and residual red clays formed from lime- 

 stone as "Richmond and Medina transition beds." The former he places in the 

 Ordovician, the latter in the Silurian, although he does not doubt that Ulrich is 

 right in placing the Richmond of Indiana in the Silurian. He states, however, 

 that in this region the strata to which he applies the name Richmond are so closely 

 associated with the underlying shales, being included with them in many weU 

 drillings, that it is not convenient to separate them from the Ordovician. The 

 strata described by Lane as Richmond and Medina consist of red and green shale, 

 with some limy beds, and vary in thickness from little or nothing to about 142 feet 

 at Cheboygan, thickening toward the south. 



Ulrich in commenting on Lane's view states that the Utica and Lorraine do not 

 outcrop in Michigan, but that the "Trenton" is succeeded by the Maquoketa, of 

 Richmond age, with a hiatus between equivalent to the Eden, Utica, and Maysville 

 of the Cincinnati section. 



L 17. MANITOULIN ISLANDS. 



The east end of Great Manitoulin Island, Ontario, falls within the area mapped 

 on the French River sheet. In reporting on that area Bell ^^ summarized the results 

 of his own work and that of his colleagues in preceding years. The several forma- 

 tions of the later Ordovician — "Chazy?, Trenton, Utica, and Hudson" — are 

 described in some detail. To the Chazy are doubtfully assigned the lowest beds of 

 the Paleozoic in this region, certain chocolate-colored marls, with some fine sand- 

 stones, 100 feet thick. Bell obtained no fossils from these strata, but Ami ^* states 

 that " Billings notes in a list of fossils from the island farthest south of the group, 

 off Point Pallideau, Lake Huron, the occurrence of Modiolopsis parviuscula, 

 Vanuzemia inconstans, Pleurotomaria staminea, and Lingula huronensis, species 

 known to occur in the Chazy of different portions of Ontario, notably in the Montreal- 

 Ottawa-Champlain basin." 



